With advances in flash memory technology, device types, and memory fabrication, the failure rate in the stores data increases. This can be attributed to the manufacturing of the memory, latent defects, or defects that grow over time causing the memory to misbehave, and physics of the device that lead to charge loss over time. This can negatively impact the endurance of the memory, the capability to retain data over period of time, and many other erroneous manifestations.
When a cluster of cells (called memory blocks) shows an increase in number of failed bits over time, and the number of failed bits consistently exceeds a specific threshold, this block is typically decommissioned. This will reduce the capacity of the storage system. Under extreme conditions, the loss in capacity, due to decommissioning of failed blocks, can bring down the entire storage system.